Recently, a hub bearing has been widely used as the bearing device of the wheel supporting portion of the vehicle (e.g. referring to Patent Literatures 1 to 3). The hub bearing is configured in such a manner that the inner ring with a flange to which the wheel is attached is supported rotatably and coaxially to the outer ring fixed to a vehicle body. The sealing device preventing the intrusion of muddy water, dust and the like (hereinafter referred altogether to as muddy water) into a bearing space or preventing the leakage of lubricant (grease and the like) filled in the bearing space is mounted on both end portions of the outer ring and the inner ring in an axial direction. The sealing device on a flange side (a wheel side, an outer side) of the bearing device for the wheel shown in Patent Literatures 1 to 3 includes a core member fitted to the outer ring, and a seal body made of an elastic material such as rubber fixed to the core member. The seal body includes a seal lip elastically contacting the inner ring directly or through a slinger (a metal ring).
In the sealing device, dust gets stuck into an elastic contacting portion of the seal lip and the inner ring when muddy water intrudes into the sealing device from a gap between the seal body and the flange portion of the inner ring. When the inner ring continues rotating under the condition that dust gets stuck into the elastic contacting portion, a distal end portion of the seal lip is worn away and a seal function of the bearing space deteriorates over time due to a mutual slidable contact between the seal lip and the inner ring. Patent Literature 1 discloses the sealing device in which the seal body includes the seal lip directly and elastically contacting the inner ring and a labyrinth lip extending into a recessed groove formed at the flange portion on the outer diametrical side of the seal lip. FIG. 2 of Patent Literature 2 illustrates a seal assembly constituted with a cover member (the core member and the seal body) fitted to the outer ring and an abutting member (the metal ring) fitted along the inner ring. The cover member has the seal lip elastically contacting the abutting member, the seal lip not contacting the abutting member, and a projecting portion provided so as to project to the outer diametrical side of the outer ring. In the cover member, a labyrinth seal is formed by a part of the abutting member, the seal lip not contacting the abutting member, and the projecting portion. Furthermore, Patent Literature 3 discloses a sealing structure constituted with the metal ring fitted to the inner ring along the flange portion and a sealing member fitted to the outer ring having the seal lip elastically contacting the metal ring. It is disclosed that the metal ring is provided on its outer diametrical side with a folding portion projecting to the opposite side of the flange portion, the outer ring (an outer member) includes an extending portion located outward in a diametrical direction from the folding portion, and a labyrinth is formed by the folding portion and the extending portion.